form.parse callback prevents form.on('part') from running

[jsainz237]

Issue: I get two different logs from the following examples, where it should make no difference

request-handler.ts - Example 1 (w/o callback)

import { Request, Response } from "express";
import form from './lib/form-handler';

export async function handleRequest(request: Request, res: Response) {
  
  // ... other code is here

  // parse form to get file(s) to upload to B2
  form.parse(request);
}

Expected output:
{ ETag: 'd9528738...', VersionId: '4_z51d4ef22801c394...' } (output from form-handler file)

Actual output:
{ ETag: 'd9528738...', VersionId: '4_z51d4ef22801c394...' } (output from form-handler file)

request-handler.ts - Example 2 (w/ callback)

import { Request, Response } from "express";
import form from './lib/form-handler';

export async function handleRequest(request: Request, res: Response) {
  
  // ... other code is here

  // parse form to get file(s) to upload to B2
  form.parse(request, (err, fields, files) => {
    console.log("hello from callback");
  });
}

Expected output:
{ ETag: 'd9528738...', VersionId: '4_z51d4ef22801c394...' } (output from form-handler file)
hello from callback

Actual output:
hello from callback

The actual output w/ a callback excludes console logs from my form.on('part) configuration in my form-handler.ts file.

---

Here is my form handler

/lib/form-handler.ts
Note: b2Client uses the aws-sdk S3() class to send data to Backblaze B2

import multiparty from 'multiparty';
import { b2Client } from './b2-client';

/** Multiparty form that handles multipart/form-data (including files from form) */
const form = new multiparty.Form();

// for each part of the file stream, send part to B2
form.on('part', (part) => {
    b2Client.putObject({
        Bucket: process.env.B2_BUCKET_NAME!,
        Key: part.filename,
        Body: part,
        ContentLength: part.byteCount,
    }, (err, data) => {
        if(err) throw err;
        console.log(data);
    });
});

export default form;

I don't think adding a callback to form.parse should prevent the form.on('part', ...) from running. Is this a bug, or am I doing something wrong?

[dougwilson]

https://github.com/pillarjs/multiparty#multipartyform

autoFields - Enables field events and disables part events for fields. This is automatically set to true if you add a field listener.
autoFiles - Enables file events and disables part events for files. This is automatically set to true if you add a file listener.

https://github.com/pillarjs/multiparty#formparserequest-cb

If cb is provided, autoFields and autoFiles are set to true and all fields and files are collected and passed to the callback, removing the need to listen to any events on form.

[jsainz237]

Ah ok I see. Thanks.